Deposition

Deposition is the process whereby sediments are

“released” or “fall out” of an erosional system.

River Delta

Glacial Moraine

Sand Dune

Barrier Island

Factors that Impact Deposition -- Velocity

The primary factor that impacts the

deposition of sediments is the velocity of the

erosional system.

The slower the erosional system, the more likely sediments

will deposit.

In addition, the slower the erosional system the more diverse the types of sediments to

be deposited.

Velo

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Eros

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Deposition

High Deposition Rate = Low Velocity

Low Deposition Rate = High Velocity

Factors that Impact Deposition -- Velocity

RT = Pg. 6

The velocity of stream has changed from 100 cm/s to 0.1 cm/s. What

type of sediments would deposit in the stream?

A stream that is moving at a rate of 100 cm/s can carry small pebbles,

sand, silt, and clay.

A stream that is moving at a rate of 0.1 cm/s can carry small silt and

clay.

This means that as the stream decreases in velocity, the small

pebbles and sand cannot be carried and will be deposited.

Factors that Impact Deposition – Characteristics of Sediments

Sediment Size

Depo

sition

rate

Depo

sition

rate

Depo

sition

rate

Sediment DensitySediment Shape (round – flat)

Large sediments deposit more quickly

than small sediments.

Round sediments deposit more quickly than flat sediments.

Sediments with a high density deposit more quickly than

sediments with a low density

Deposition of Dissolved Substances.

Some sediments are dissolved in water.

Dissolved sediments are commonly found in stream and tidal erosion systems.

In order for dissolved sediments to be be deposited, the water in solution needs to be evaporated. The remaining sediments would then deposit out of the

system.

As this lake evaporates, the salt is deposited. Minerals which precipitate as a result of the evaporation of water in solution are known

as evaporites.

Minerals are deposited from solution of water that drip into

underground caverns.

Deposition by Gravity (Mass Movement) Sediments that are deposited

from a mass movement event (Ex: avalanche,

mudflow, rockfall) tend to deposit quickly.

The sediments deposited are usually found in a pile at the base of the erosional system.

The sediments tend to be varied in shape and size and are unsorted and unlayered.

Deposition by Streams

HORIZONTAL SORTING: As the stream empties in to the ocean (mouth), the velocity decreases. Sediments will settle out of the stream as they enter into the ocean. (Larger sediments closer to the mouth of the stream – smaller sediments further out into the

ocean.

Deposition of sediments in a stream will take place when the

velocity of the stream decreases.

The deposition of sediments can take place in many areas of the

stream.

Mouth of the Stream

Deposition by Streams

Meanders

Stream velocity changes as water moves through the meanders of a stream.

The stream velocity (kinetic energy) of the stream is high on the outer edges of the stream.

HIGH EROSION

The stream velocity (kinetic energy) of the stream is low on the inner edges of the stream.

HIGH DEPOSITION

AREAS OF DEPOSITION

Deposition by Streams

Levees and Floodplain

Levee

Floodplain

Stream discharge: The amount of water (volume) that passes through

a given point in a stream.

At times, the discharge of a stream increases. This may happen during

heavy precipitation or sudden, significant snowmelt. This will lead

to flooding.

When flooding occurs, water flows over the banks of the stream. The

sediments carried by the water also flow over the stream banks.

These sediments can deposit quickly into mounds found on the

edges of the stream bank (levee) or throughout the land surrounding

the stream (floodplain).

Deposition by Streams

Graded Bedding – Stream to Lake Deposit

Sudden stream flow into a lake creates turbidity currents.

Flooding events may also create a sudden increase in discharge from a stream into a

lake.

The increased discharge creates turbidity currents (a swirling mixture of various size

sediments).

Sediments will deposit at the lake bottom in graded beds. Graded bedding is the sorting

of sediments by size. Larger sediments settle out first followed by smaller

sediments.

Larger sediments settle out by size from largest (bottom) to smallest (top).

Series of graded beds can provide scientists with clues as to the number of flooding events that have occurred in the

lake.

Deposition by Wind Sediments are deposited out of the

wind as the wind velocity decreases.

Most sediments deposited out of the

wind are sand-sized or smaller.

The wind can deposit small sediments over a

large area.

Sand is deposited in windy environments in the form of sand dunes.

Wind direction

Windward side of the dune =

GENTLE SLOPE

Leeward side of the dune =

STEEP SLOPE

Deposition by Glaciers Sediments are deposited out of a

glacier as the glacier moves

across a landscape and/or as the glacier

melts.

Most sediments deposited out of glaciers are of

assorted sizes and origins. Sediments

deposited by glaciers are most usually angular,

sub-rounded, polished and unsorted.

Glacial deposits = Unsorted, angular, sub-rounded, polished

Drumlin= A collection of unsorted sediments released by a glacier. The steep end of the drumlin points towards the direction the glacier came from.

Deposition by Glaciers As a glacier moves across a landscape it is continually depositing sediments. Assorted sediments that are

deposited underneath a glacier as it moves

becomes part of the ground moraine.

The pile of sediments found in front of a

glacier -- pushed by the glacier will become a

terminal moraine.

Ground moraines can be found throughout much of upstate New York.

Terminal moraines make up the composition of

Long Island.Terminal Moraine

Ground Moraine (under glacier)

Long Island MorainesThe last major Ice

Age led to the advance and retreat of large continental glaciers the covered

much of the northern US

(between 60,000 to 40,000 yrs ago).

The retreat and melt of the glacier created two

terminal moraines that make up of the topography of Long

Island.

Deposition by Tides The waves drag

along the bottom of the sea as they

approach the shoreline.

This action will pull sediment

from the sea floor.

This sediment may then deposit

along the shoreline in the form of a beach.

Deposition by Tides

A projection from the shoreline into the ocean, such as a pier, groin or jetty can impact how sediments are deposited on a beach.

As the current moves towards the groin, its velocity slows down causing sediments to deposit more rapidly. High deposition rates are found on the side of the groin

facing the current.

The opposite side of the groin encounters unusually high erosion rates because the sand is not there to protect the beach from the currents.

Movement of

longshore current

Deposition by Tides Barrier Islands

Strong storms can cause heavy erosion to occur along a beach. Much of the sediment on a beach may be carried

back out to sea during a strong storm. The extra sediment carried out to sea can deposit as a sandbar. If this sandbar rises

above the sea, a layer of soil may develop

along with vegetation and create a barrier

island.

Barrier islands help to protect coastlines from strong storm surges,